This invention relates to an imido-modified unsaturated polyester resin composition usable for coil-impregnation, electric wire-coating, casting, adhesives in a transform built in domestic electric devices, computors, office automation instruments, etc.
Recently, insulating varnishes with improved heat resistance and improved mechanical properties have increasingly been required, as electric devices have become miniatuarized and lightened and as working conditions have been made severe. Conventional heat resistant compositions usable for coil-impregnation include silicone-, diphenyl ether- and polyamide types. However, all of these are solvent type-varnishes, which require troublesome and lengthy processing for varnish-treatment. For a polyamidoimido-type varnish, there may be used only a polar solvent such as N-methylpyrrolidone and N,N-dimethylacetamide, which are expensive, and there has been a fear that these solvents have an adverse influence on insulating materials used in electric instruments due to their high solvency power. As heat-resistant resins other than those described above, there have been known an imido-modified unsaturated polyester resin obtainable by incorprating into an unsaturated polyester system an imido compound obtained by reacting a polyvalent carboxylic acid anhydride such as trimellitic anhydride and pyromellitic dianhydride with a diamine in an organic solvent, in which heat resistance has been improved as compared with conventional unsaturated polyester resins (Japanese Patent Publication No. 28509/1980). In addition to the above described resins, there has been known an imido-modified unsaturated polyester resin, whose heat resistance has been improved by employing a divalent glycol compound having an imido group in the molecule as one of the components of the polyhydroxy alcohol during synthesis of the unsaturated polyester (Japanese Patent Publication No. 8995/1976). However, these resins can only be prepared according to a complicated synthesis process in which an imido compound is first synthesized and an unsaturated polyester is then synthesized as a part of an alcohol or an acid. Therefore, the resulting imido-modified unsaturated polyester resins cannot be said to sufficiently satisfy the present commercial requirement, although the heat resistance thereof has been improved. Polyhydroxy alcohol component other than those described above include an imido-modified polyester resin in which tris-(2-hydroxyethyl)isocyanurate is reacted therein, as a polyhydroxy component (Japanese Patent Publication No. 33146/1970).
There has also been known a saturated polyester in which a divalent alcohol functioning as the polyhydroxy alcohol component and having an imido ring, obtainable by a reaction of 1,2,3,4-butanetetracarboxylic acid or an acid anhydride thereof with an amino-alcohol is reacted singly or in combination with another alcohol (Japanese Unexamined Patent Publication No. 72296/1973). However, the technique described above is only applicable to a varnish for an enamelled copper wire and it is impossible to apply such a technique to a varnish for coil-impregnation due to insufficient compatibility with a polymeric monomer.
Any of the unsaturated polyester resins described above cannot be said to have sufficient compatibility under heat deterioration when used in enamelled wires, although the heat resistance thereof has been improved.